One of the responsibilities that a municipal waste landfill owner/operator faces is the management of landfill-generated gas. Landfill gas is a by-product of the anaerobic decomposition of the biodegradable constituents of the landfilled waste. The primary components of landfill gas are Methane (CH.sub.4), and Carbon Dioxide (CO.sub.2). Methane carries the potential hazard of accumulating in uncontrolled void spaces and, if ignited, causing a fire or explosion. The explosive range of methane is five to fifteen percent in air by volume (5-15% vol. air).
Landfill gas management practices involve installing extraction devices such as vertical extraction wells or horizontal trenches in the waste mass and capturing and conveying the gas to a combustion or energy recovery facility. Modern-day landfills also employ the use of impermeable liners to contain landfill gas and other landfill-generated fluids. However, many older landfills exist where there was an inadequate containment system or there was no containment system installed, and the release of the gas can pose a potential threat to the environment. As the gas is generated, a pressure gradient is established, and the gas begins to migrate in the direction that offers the least resistance to flow. Since the waste is usually deposited in layers, or lifts, and daily cover is usually specified to minimize gaseous emissions and odors, the potential pathway of least resistance to gas flow is often lateral. Consequently, gas sometimes escapes (migrates) into the surrounding soils and rock formations. Gas monitoring wells are installed in these soils to track the potential migration of landfill gas. The occurrence of methane in the perimeter gas monitoring wells is the reference point to which the effectiveness of most gas management systems is measured.
The present invention provides a method of altering gas migration to an extent that the extraction devices can reverse the direction of gas flow in the soil and rock formations, and eliminate offsite landfill gas migration. The preferred procedure involves the injection of a fracturing fluid and propping agent into the zone of influence under sufficient pressure to induce new fractures and propagate existing fractures, bedding planes and lithologic discontinuities. These new fractures connect those areas where a draw exists from an active extraction well with fractures that contain gas.